Swift Heavy Ion-Induced Chemistry of CH ₃ CN Ices at 10 and 80 K

Acetonitrile (CH₃CN) is a key nitrogen-bearing molecule detected in a variety of astrophysical environments and is considered a potential precursor of prebiotic compounds. The study aimed to investigate the stability and radiation chemistry of ⁵⁶Fe¹⁰⁺ ions at the Grand Accélérateur National d'Ions Lourds (GANIL). In situ FTIR spectroscopy revealed efficient molecular destruction accompanied by the formation of several nitrogen-bearing species, including HCN, H₂CCNH, CH₂CHNC, CH₃CHNH, H₂CNH, NCCN, and NH₃ with possible contributions from the C-H such as CH₄ and C-H stretching of HC₃N and, to a lesser extent, the N-H stretch of ketenimine (H₂CCNH). The apparent destruction cross section of CH₃CN was found to be (2.3 ± 0.8) × 10^-12 cm² at 10 K and (5.6 ± 1.0)×10^-12 cm² at 80 K, indicating more extensive radiolytic processing at higher temperatures. Enhanced radical mobility at 80 K promotes hydrogenation and polymerization, leading to a refractory C-N-rich residue, whereas at 10 K intramolecular isomerization dominates. These results demonstrate that swift heavy-ion irradiation of nitrile ices efficiently produces small nitriles, isonitriles, and polyimines of astrochemical interest, supporting the role of CH₃CN as a hidden precursor to prebiotic organic matter in interstellar and planetary ices.